The present invention relates generally to systems and methods for transmission power control in communication systems and, more particularly, to systems and methods for forward link power control in radio-communication systems.
Forward link power control has conventionally been implemented in a number of radio-communications systems, including, for example, the CDMA2000 and WCDMA systems. In such systems, forward link power control is used to combat Rayleigh fading of the forward link propagation channel at slow mobile terminal mobility. Due to the motion of the mobile terminal and/or the surrounding environment, the forward link propagation channel gain increases or decreases continuously. The signal-to-interference ratio (SIR) of the signal received at the mobile terminal, therefore, will also change according to the changes in the forward link propagation channel gain.
The following description pertains to the CDMA system as an example. In CDMA2000, when forward link power control is used, the base station sends a target frame error rate (FER) for the forward traffic channel to the mobile terminal when forward link power control is used. The mobile terminal then maps the target FER into the target SIR that is required to achieve the target FER. Subsequent to determining the target SIR, the mobile terminal estimates the received SIR over substantially the entire duration of each power control group of the forward link and sends power control bits (PCBs) to the base station multiplexed on the reverse pilot channel. If the received SIR is below the target SIR, the mobile terminal sends a power control bit with a value of +1 to request a power step up. If the received SIR is equal to, or above, the target SIR, the mobile terminal sends a power control bit with a value of −1 to request a power step down. In response, the base station may increase or decrease the power of the forward traffic channel assigned to the particular mobile terminal by a value ΔP. The base station maintains the transmitted power at the new power value for a period T, equaling the duration of a power control group, until the base station receives a new PCB from the mobile terminal.